Centralized traffic controlling system for railroads



W. T. POWELL Sept. 26, 1939.

CBNTRALIZBD TfikiFiC CONTROLLING SYSTEM FOR RAILROADS Filed June 16, 1936 5 Sheets-Sheet 1 co +d+n 2. we ELu+cH 3 9 oL+cou J11 ATTRZiEY Sept. 26, 1939.- w. T. POWELL 2,174,291

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed June 16, 1936 5 Sheets-Sheet 2 Confrols; d1 Q m 0; D o

TToRNY l k- W 1 \Jewm lk a) Sept. 26, 1939. w. r. POWELL CENTRALIZED TRAFFIC CONT ROLLING SYSTEM FOR RAILROADS Filed June 16, 1936 5 Sheets-Sheet 3 On IndiccLl'ions Sept. 26,1939. w. T. POWELL CENTRALIZED TRAFFIC CONTROLLING SYSTEI FOR BAILROADS s SheetS-Shet 5 Filad June 16, 1936 pfi as to R Patented Sept. 26, 1939 UNITED STATES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Winfred T. Powell, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application June 16, 1936, Serial No. 85,531

8 Claims.

This invention relates to centralized traffic controlling systems for railroads and it more particularly pertains to means for transmitting, receiving, storing and executing controls and indications in a communication system of the multiple impulse or coded type.

In such a system, the switches and signals are distributed throughout the territory, with those located relatively near or adjacent each other,

together with the apparatus provided to govern these switches and signals, conveniently referred to as comprising a field station. lhe communication system interconnects the control ofiice and the several field stations and it is so organized 5 that complete control and supervision of the various switch and signal devices at the remote stations are obtained by the operator. Such a traffic controlling system is supplemented by the usual automatic block signal system and other 20 local means ordinarily provided to guard against unsafe train movements, improper operation of track switches and the like.

In accordance with the present invention the communication system comprises a two-wire line circuit extending from the control office through the several field stations in series. The conductors of this line circuit are conveniently referred to in the specification and identified in the drawings as line conductor L and return conductor R. The two-wire line circuit is normally de-energized, with a source of direct current normally connected to the line circuit in the control oilice and with the line circuit normally maintained open at the end field station. The line relays and other devices are connected in series with the line wires at the control ofiice and at the various field stations, with the L and R. conductors connected together at the end field station during transmission to provide a closed circuit loop.

The circuits are so arranged that any field station in the series may initiate the communication system into a cycle of operations by energizing the normally de-energized line circuit and during such a cycle indications are transmitted from the initiating field station to the control ofiice. These indications comprise impulses of alternating current or" normal and reverse phase, together with the absence of alternating current, which make up a code combination for registering the transmitting station in the oflice and for the transmission of indications in accordance with track and signal conditions at the registered station.

The circuits are so arranged that the control ofiice may initiate the operation of the communication system by applying a short impulse of alternating current to the iine circuit. During such a cycle of operations polar impulses are 60 transmitted in the form of a code which is effective to select a desired station and to transmit controls thereto.

The system is of the duplex type, that is it is operated through separate cycles of operations, during each of which transmission of controls and/or transmission of indications may occur. When controls are transmitted a station selective code is first applied to the line circuit for selecting the particular station with which communication is desired and then the controls are 10 transmitted to that station. When indications are transmitted the particular field station transmitting such indications first transmits a station registering code for identifying this station in the ofiice and then the indications are transmitted from this station to the oifice.

For the transmission of controls a predetermined number of impulses of selected polarities are applied to the line circuit, each impulse operating step'by-step apparatus in the control ofiice and at the field stations in synchronism through a cycle of operations, irrespective of the character of the impulses. The impulses and the time spaces between are all substantially of equal duration.

For the transmission of indications a predetermined number of impulses are applied to the line circuit for operating the step-by-step apparatus in the office and at the transmitting field station through a cycle of operations. During such a cycle, alternating current is or is not superimposed on the line circuit during the impulses and during the time spaces between impulses and the phase relation of this alternating current is reversed, with respect to its connection to a registering device in the control ofiice, for making up the indication code combinations.

For convenience in describing the operation of this system the periods during which the line is energized by the impulses applied in the control oiiice from the source of direct current will be referred to as the on periods and the de-energized periods or time spaces between direct current impulses will be referred to as the off periods.

A system arranged in this manner provides for the transmission of a comparatively larger number of indications than controls at each step of the stepping mechanism. Since control codes are made up of either or impulses during each on period and since the off periods are provided for stepping operations, a choice of two controls per step is provided. As will be pointed out later in detail, a choice of six indication codes is provided for each step of the stepping mechanism, three of which are provided for each off period and three of which are provided for each on period. These codes are first, no alternating current superimposed on the line circuit, second, alternating current of normal phase superimposed on the line circuit and 0 third, alternating current of reverse phase superimposed on the line circuit.

At the start of a cycle of operations for the transmission of controls, a short impulse of alternating current is applied to the line circuit, followed by a short positive energization of the line circuit for conditioning the apparatus at the control office and at the field stations. Following the conditioning period a number of of? and on periods are provided, as determined by the number of stepping relays, which number is in turn determined by the size of the system.

At the start of a cycle of operations for the transmission of indications the normally de-energized line is energized with negative polarity, followed by a short impulse of alternating current, after which the line is energized momentarily with positive polarity. A number of off and on periods then follow, the number of which is determined as above mentioned by the size of the system.

Other objects and advantages of the present invention will be hereinafter set forth in the specification and claims and further details will be better understood by referring to the accompanying drawings which illustrate one method of carrying out the invention by way of example.

The drawings illustrate in diagrammatic manner the apparatus and circuits employed. For convenience in describing the invention in detail those parts having similar features and functions are designated in the diiferent figures by like reference characters, generally made distinctive either by the use of distinctive exponents representative of their location in the system or by the use of preceding numerals representative of the order of their operation. It has been found convenient to illustrate contacts of certain relays on two different sheets of drawings and in this case the circuits which control these relays have been shown connected to full line blocks, with these same relays indicated on an adjacent drawing by dotted line blocks. For this reason certain reference characters have been repeated on some of the drawings but only where they refer to the same relay on another drawing. The polyphase motor type relay M is illustrated in the upper portion of Fig. in, while the contacts of this relay and the circuits which they control are illustrated in the lower portion of Fi 1 Fig. 1 illustrates the line circuit arrangement for the control office and an intermediate field station with a small portion of the end field station illustrated, this figure including only the apparatus most closely associated with the line circuit.

Figs. 1A and 1B illustrate the apparatus and circuit arrangement employed in the control office for providing means whereby the operator may govern the switches and signals throughou':v an extensive territory and whereby indications may be received from various field stations throughout such territory. For convenience in considering the control office circuits, Fig. 13 should be placed below Fig. 1A with correspondingly numbered lines in alignment.

Figs. 2 and 2A illustrate the apparatus and circuit arrangement employed at a typical field station for providing control of a track switch and associated signals and for transmitting indications to the control oflice in accordance with the present invention. A portion of the field station apparatus at the end station is also shown in Fig. 2A to illustrate the manner of terminating the two-wire line circuit at the end of the line. For convenience in following the circuit operation of the system Fig. 2 should be placed to the right of Fig. 1A and Fig. 2A should be placed to the right of Fig. 2 with correspondingly numbered lines in alignment.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of direct current and the circuits with which these symbols are used always have current flowing in the same direction, that is from to The symbols (38+) and (B) are employed to indicate the positive and negative terminals respectively of a suitable battery or other source of direct current having an intermediate tap (CN) and the circuits with which these symbols are used may have current flowing in one direction or the other depending upon whether the terminal B+) or (B) is used in combination with tap (ON).

Control ofiice equipment.-The control office (Figs. 1A and 13) includes a control machine having a group of control levers for each field station, a miniature track layout corresponding to the track layout in the field and various indicating lamps or equivalent devices, together with apparatus and circuits to accomplish the desired operation of the system.

That part of the control office illustrated shows more particularly the portion of the control machine which is typical of the apparatus for selecting any one of a plurality of field stations, for transmitting controls to a selected station, for registering the identity of a transmitting field station in the control office and for receiving indications transmitted from a registered station.

The illustrated apparatus includes a starting button SB associated with a particular station, which starting button controls the operation of a storing relay SR and a code determining relay CD associated with the same station. It will be understood that there will be a starting button and associated SR and CD relays for each station in the system. The apparatus for controlling the operation of a track switch has been illustrated and comprises switch machine lever SML. One or more signal control levers are likewise provided, but for convenience these levers are not illustrated, since the control of the switch machine by lever SML is typical of the control of signals by a signal control lever.

A plurality of code jumpers are selected by the circuits controlled by the CD relays and those illustrated by reference characters l8 and ll, selected by the illustrated CD relay, are for the purpose of applying a station selecting code to the line circuit in response to the initiation of the operation of the system when the associated starting button is actuated.

Starting relay STR is for the purpose of initiating a cycle of operations in response to a field station start. Code sending relays PC and NC are for the purpose of providing the proper polarity of energization of the line circuit during the transmission of control impulses. With relay PC up and relay NC down, a impulse is applied to the line from battery LB when the impulsing relay effects the closure of the line circuit. With relay NC up and relay PC down a impulse is applied to the line circuit.

Pilot relays EPT and 21 T are of the biased-toneutral type and are positioned in accordance with a station identifying code received in the control office during a duplex cycle or a cycle during which indications alone are tranmitted.

Station relay ST is assumed to be associated with the station illustrated in Fig. 2, it being picked up in response to the station identifying code transmitted by this station. It will be understood that there is a separate ST relay for each station to be registered in the control ofiice, these relays being selected by the different positions of the pilot relay contacts. Indication receiving relays IIR. and HR are also of the biased-toneutral polar type and are positioned in accordance with the indications transmitted from a registered station during a cycle in which indications are transmitted. Relays IAX to AAX inclusive are auxiliary relays cooperating with the pilot relays and the indication receiving relays for a purpose which will be fully explained.

Message relay M is of the polyphase motor type comprising stator windings 3, 4 and and a rotor 6 which actuates contact finger I. Winding 4 is the indication receiving winding, it being connected in the line circuit for receiving superimposed alternating current impulses. Winding 3 is a neutralizing winding for neutralizing the efiect of direct current applied to the line circuit from battery LB so that the direct current impulses will have no effect on the operation of relay M. Winding 5 is the polarizing winding which is permanently supplied with alternating current from the same source which is reversibly connected to the line circuit during a cycle of operations. It will be noted that the polarizing winding is connected to the alternating current supply comprising conductors l and 2, which supply is also reversibly connected to the line circuit by a transmitting field station. When alternating current is sent through winding 4 of relay M in one phase, rotor 6 is actuated in one sense. When current is sent through winding 4 in the opposite phase, rotor 6 is actuated in the opposite sense. When there is no current in winding 4, no current in polarizing winding 5 or none in either winding the relay is de-energized and the rotor assumes its neutral position as illustrated in Fig. 1A. The relay therefore provides for three positions based on shifting the phase of current in the line circuit and absence of current in the line circuit, For convenience these relay positions will be referred to as normal with the contact in its right hand position, reverse with the contact in its left hand position and neutral with the contact in its mid-position.

Line relay F is included in the line circuit at the cfiice and is for the purpose of repeating each energization and de-energization of the line from battery LB, irrespective of the polarity of such energization. Line repeating relay FP repeats each energization and de-energization of relay F during a cycle of operations. Slow-acting relays SA and SAP are picked up at the beginning of each cycle, remain up throughout the cycle and are dropped at the end of the cycle. Auxiliary relay AX is for the purpose of making the first on period the same length as the other on periods of a cycle. Impulse relays IE and are for the purpose of timing the closure and opening of the line circuit during a cycle of operations and as will be apparent from the detailed description which follows, the on and off periods during which controls and indications are transmitted are all of substantially the same length.

Associated with the line repeating relays is a bank of stepping relays including relays IV, 2V, 3V together with a half-step relay VP and a halfstep repeater relay VPR. This bank of stepping relays is for the purpose of marking off the successive steps of each cycle, the stepping relays being successively picked up during the off periods and relay VP being shifted in position during each on period. Relay VPR is provided to make the execution periods (later described) during the on periods of the same length as the execution periods during the oil periods.

Condenser 2C is for the purpose of providing a by-pass or low impedance path from line L through winding 4 of relay M to line R for the purpose of preventing alternating current applied to the line circuit during the transmission of indications from flowing through line relay F and battery LB. In this connection, it will be assumed that relay F in the control office and the F relays at the field stations, each of which is bridged by a condenser such as 20 shown in Fig. 2, have sufficient impedance to the frequencies of alternating current used so that it will be bypassed around these relays through the condensers. It will be obvious that separate impedance coils or parallel resonant traps may be inserted in series with the F relays and bandpass filters may be used in place of the illustrated condensers to furnish a low impedance path around the relay windings. It will furthermore be assumed that the direct current resistances of the transformer winding included in the line circuit at a transmitting station is low, as well as the direct current resistance of windings 3 and 4 of relay M.

Field station equipment-The field station illustrated in Figs. 2 and 2A is typical of all stations of the system and may be adapted for use at the first, second or any other location by merely altering certain code jumpers to provide for the desired codes. For convenience in the description, this field station has been specifically illustrated as being the first of the series by reason of the distinctive exponents employed. Likewise the end station illustrated in Fig. 2A is assurned to be the second in the series by reason of the distinctive exponents employed, but it will be understood that other stations may be interposed between the office and the first station and between the first station and the second station.

A track section is illustrated, having track switch TS which is operated from one extreme locked position to the other by means of switch machine SM which is in turn controlled by switch machine control relay SMR Suitable signals are associated with the illustrated track section for governing traffic thereover and are governed from the control ofiice through the medium of the communication system by signal control relay SGR These signals and their control by relay SGR have been omitted for the sake of simplicity. These control relays are of the two-position polar'nagnetic-stick type and are governed from the control office through the medium of the communication system. Relay SMR controls the operation of the associated switch machine by energizing its normal or reverse operating wire from a local source of current when its polar contact is actuated to right and left positions respectively.

For the purpose of illustrating how indications are transmitted for registering a field station at the ofiice, code jumpers H0 and ill are provided. For the purpose of indicating how indications are transmitted from a registered station during the on periods, switch machine repeating relay WP is illustrated, it being understood that this relay, with its contacts in the positions illustrated, repeats the track switch in its normal locked position. With its neutral contact l M! dropped away, it repeats the track switch in its unlocked position and with neutral contact MP3 picked up and polar contact l4! in its left hand dotted position it repeats the track switch in its reverse locked position.

For the purpose for indicating how indications are transmitted from a registered station during the oii periods relays M RD and LD are illustrated. It will be assumed that relay M is picked up to indicate that all signals associated with the illustrated track section are at stop. Relay M dropped and relay RD picked up indicates signals cleared for trafiic in a right hand direction, and relay M dropped away and relay LD picked up indicates signals cleared for trafiic in a left hand direction.

The communication part of the system includes polar line relay F and its quick acting repeating relay FP Slow-acting relays SA and SAP correspond to similar relays in the control office and are for a similar purpose, that is they define the bounds of a cycle of operations by being picked up in sequence at the beginning of a cycle and dropped in sequence at the end of a cycle.

The field station includes a bank of stepping relays comprising relays lV 2V 3V and VP which correspond to similar relays in the control omce. These relays are operated by circuits similar to the circuits for corresponding relays in the office and in synchronism therewith, therefore it is believed unnecessary to indicate the detailed circuits of the field station stepping relay bank. Dotted line I 42 illustrates that these re lays are controlled by relays FF and SAP in a manner similar to the control of the ofiice stepping relays.

For the purpose of illustrating the selection of a station for the transmission of controls, relay S0 is shown. It is selectively controlled by code jumpers !20 and I2l, connected at the station illustrated, to make this station selectively responsive to a station selection code of on the first two steps.

Relays IBZ and ZBZ are for the purpose of transmitting alternating current impulses during the off periods of normal and reverse phase respectively. With both of these relays down during an ofi period no alternating current is transmitted. Relays IFZ and ZFZ are for the purpose of transmitting alternating impulses of normal and reverse phase respectively during on periods. With both of these relays down during an on period no alternating current is transmitted. Transformer TF is for the purpose of applying the alternating current from buses l and 2 to the line circuit when such alternating current is to be transmitted. Condenser lC in series with the primary winding of transformer TF is for the purpose of obtaining a balance in the phase relation between the primary and secondary circuit of this transformer, when such balance is required.

A field change relay CH is illustrated to indicate how a cycle of operations is initiated from a field station. For the purpose of illustrating the manner of determining when a field station is to transmit its indications, lock-out relay L0 is employed. When relay L0 is picked up during a cycle of operations to permit the field station to transmit, relays IBZ, ZBZ, IFZ and ZFZ are rendered active for applying or not applying alternating current impulses during the succeeding ofi and on periods.

Start relay STR is provided to receive the initiating alternating current impulse applied to the line circuit in the control ofiice at the beginning of a cycle of operations. Full-wave rectifier FWR is connected in circuit with the upper winding of the look-out relay for translating the initial alternating current impulse into direct current for the purpose of maintaining the lock-out relay energized only at the transmitting field station in a manner which will be pointed out in detail.

It is believed that the nature of the invention, its advantages and characteristic features will best be understood with further description being set forth from the standpoint of operation.

Operation The system of the present invention is normally in a condition of rest, from which it may be initiated into a cycle of operations either from the control office or from any one of the field stations when there are new controls or new indications respectively ready to be transmitted. If new controls for several diiferent field stations are ready for transmission at substantially the same time they are transmitted on separate cycles, one station for each cycle. Similarly if several field stations have indications ready for transmission at the same time they are transmitted from such field stations to the control ofiice, one station for each cycle.

It may happen that there are new controls and new indications ready to be transmitted at the same time and in such instances controls are transmitted to a selected field station simultaneously with the transmission of indications from the same or some other field station during the same cycle.

During a cycle of operations initiated for the transmission of indications alone the character of the impulses placed upon the line circuit is such that no station will be selected, these impulses merely causing the step-by-step operation of the control office stepping relay bank and the various field stations stepping relay banks. A series of impulses which selects no station for an out-bound call is referred to as a control phantom code. Such a code in the present embodiment comprises a series of impulses, the number of which is determined by the number of station selection steps.

When a cycle of operations is initiated from a field station a plurality of impulses are placed upon the line circuit at the control ofiice to cause the step-by-step operations of the stepping relay banks and these impulses and the time spaces between have superimposed thereon alternating current impulses making up a code determined by the field station which is transmitting and by the indications transmitted from the transmitting station.

During a control cycle when no indications are being transmitted no alternating current impulses are applied to the line circuit during any of the on and off periods of this cycle. A series of on and oil periods with no alternating current impulses during a cycle must register no station in the office for an inbound call and such a code is referred to as an indication phantom code. The number of impulses making up the indication code is of course determined by the number of station registration steps provided to take care of the number of stations in the system.

Normal at rest conditions-The two-wire line is normally de-energized and most of the relays in the oflice and at the field stations are normally de-energized. An exception is relay 21R. in the control office (see Fig. B) which is illustrated with its polar contacts positioned to the left, it being assumed that the previous switch indication received from the associated station indicated that the associated track switch was in its reverse locked position. Contact of relay HR in its left hand position energizes lamp RL over an obvious circuit to display such indication. Relay 21B. is maintained stuck in this position over a circuit extending from (CN), back contact 9| of relay 4AX, lower winding of relay 21R and contact 92 of relay HR in its left hand position to (3-). Relay NC is energized over an obvious circuit completed at back contact 65 of relay SA.

At the field station, relay CH is assumed to be normally energized over a circuit not shown and it will be assumed that this relay is deenergized when the associated field station has new indications to transmit. It will be assumed that the track switch illustrated in Fig. 2A is in its normal locked position, therefore relay WP with its contacts in the positions illustrated repeats this condition. It will be assumed that a signal is cleared for traific to proceed in a left direction over the illustrated track section and relay LD is illustrated in its picked up position as an indication of this condition.

Manual start.For the purpose of explaining the operation of the present system it will be assumed that lever SML is actuated to its right hand normal position for operating the associated track switch illustrated in Fig. 2A to its normal locked position and that starting button SE is actuated to start the cycle of operations. The actuation of button SB closes an obvious circuit for picking up relay SR and this relay 'closes an obvious stick circuit for itself at its front contact l2. A circuit is now closed for picking up relay CD which extends from back contact I3 of relay IE, back contact IA of relay SA, front contact I5 of relay SR, back contact l6 and winding of relay CD to Relay CD closes a stick circuit for itself extending from front contact I! of relay SR, front contact I6 and winding of relay CD to The opening of back contact l5 of relay SR, which back contact leads to a contact finger similar to contact finger I5 of the next SR relay in the series, prevents the picking up of the CD relay associated with this next SR relay in the event that another starting button is actuated to store the condition that another station is to be selected. In other words contact I5 of relay SR and similar contacts of other SR relays permit the energization of only one CD relay at any one time, even though two or more SR relays are picked up. A circuit is now closed for picking up relay SA which extends from back contact I8 of relay IV, back contact I9 of relay VP, front contact 29 of relay CD and winding of relay SA to Relay SA closes an obvious pick-up circuit for relay SAP at front contact 2I.

Because of the slow-acting characteristics of relay SAP a relatively long time interval will elapse between the picking up of relay SA and the picking up of relay SAP. During this time interval an impulse of alternating current is applied to the line circuit over a circuit extending from alternating current supply bus I, back contact 22 of relay 2E, back contact 23 of relay SAP, front contact 24 of relay SA, back contact 25 of relay IE, line conductor L, condenser C (see Fig. 2) upper winding of relay STR back contact I I2 of relay SAP line conductor R, front contact 26 of relay SA, back contact 21 of relay SAP and back contact 28 of relay 2E to alternating current supply bus 2. It will be obvious that the picking up of relay SAP disconnects the source of alternating current from the line at back contacts 23 and 27. Furthermore, this alternating current flows over line conductor L to all other stations in the system by way of back contact iii of relay SAP (and similar back contacts of the SAP relays at other stations), line conductor L through a condenser similar to C at each field station, through the upper winding a relay similar to STR at each station and through a back contact similar to H2 of relay SAP at iield station to the return line conductor. This effects the picking up of the STR relays at all stations.

The STR relays all close stick circuits for themselves similar to the one illustrated in Fig. 2 and which extends from back contact H4 of relay SAP front contact H5 and lower winding of relay STR to It will be understood that the windings of the STR relays are so de signed that the ampere turns in their stick windings are sufficient to maintain these relays in their energized positions during the reversals of the alternating current through their upper windings, so that the flux produced by current in the upper winding in opposition to that produced by current in the lower winding will be insufficient to kick the relay down.

The SA relays at the field stations are picked up over circuits similar to that illustrated in Fig. 2 and which extends from front contact llli of relay STR and winding of relay SA to and the SAP relays are picked up over obvious circuits similar to that closed at front contact Ill of relay SA The S0 relays at all stations are picked up over circuits similar to that illustrated in Fig. 2 and which extends. from (CN), back contact H8 of relay SA front contact N5 of relay STR and lower winding of relay S0 to (13-) and stick circuits are closed by the picking up of the SA relays similar to that extending from (CN), front contact II8 of relay SA front contact I22 of relay S0 back contact I23 of relay FP and lower winding of relay S0 to (B). It will be later explained how the SO relay at the desired station is selected by remaining picked up, while those at other stations are dropped out during the cycle.

As above mentioned, the picking up of the SAP relay in the office disconnects the alternating current source from the line circuit. The line remains de-energized until the SAP relay at the end station is picked up to complete the closed circuit loop at its front contact 2 l2. Relay SAP closes a pick-up circuit for relay AX which extends from back contact 98 of relay VP, back contact 99 of relay IV, winding of relay AX and front contact 299 of relay SAP to Impulsing and stepping operations-It will first be assumed (and later explained) that the PC and NC relays are positioned during the conditioning and each off period of the cycle, so that one or the other of these relays will be picked up for supplying current to the line circuit from battery LB during the on periods. It will be assumed that relay PC is picked up during the conditioning period for making the conditioning on impulse that relay NC will be picked up during the first off period for making the first on impulse that relay PC will be picked up during the second off period for making the second on impulse (-1-) and that relay PC will be picked up during the third off period for making the third on impulse (-1-).

With relay PC up and relay NC down the line circuit is energized with a impulse over a circuit which extends from the (-1-) terminal of battery LB, front contact 35'? of relay PC, back contact iii of relay NC, winding of relay F, front contacts 23 and 2 of relays SAP and SA respectively, back contact 25 of relay IE, line conductor L, winding of relay F (and similar line relays at other stations) line conductor L winding of relay F front contact 262 of relay SAP line conductor R back contact I63 of relay L0 (and similar back contacts at other stations), front contact IE2 of relay SAP (and similar front contacts of the SAP relays at other stations), line conductor R, front contacts 26 and 2? of relays SA and SAP respectively, windings and 3 of relay M, back contact 32 of relay NC and front contact 33 of relay PC to the terminal of battery LB.

Current flowing over the line circuit picks up line relay F in the control ofiice and the line relays at all field stations. A circuit is closed for picking up relay FP which extends from (-1-), front contact 34 of relay F, front contact 35 of relay SA and winding of relay F1 to The FP relays at the field stations are picked up by circuits similar to that illustrated in Fig. 2 which extends through polar contact 524 of relay F in either position.

It will now be explained how the stepping relays, the half-step relay and the impulsing relays in the control office are operated and, although the circuits are not shown, it will be obvious that the stepping relays and the half-step relays at all field stations are operated over circuits similar to those in the control office. It will likewise be understood that the FP relays at all stations follow the impulses in the line circuit as repeated by the F relays because of contacts similar to contact I24 of relay F With relay FP picked up during the conditioning on period, a circuit is closed for picking up relay VP which extends from (-1-), front contact 29 of relay SAP, front contact 3!) of relay FP, back contact 38 of relay IV and winding of relay VP to Relay VP closes a first stick circuit for itself at its front contact 3? which is independent of front contact 39 of relay FP. Relay VP opens the above described energizing circuit for relay AX at back contact 98 and relay AX drops. A circuit is now closed for picking up relay lE which extends from (-1-), front contact of relay VP, back contact MI of relay 2E, winding of relay iii and back contact 4| of relay AX to The picking up of relay lE opens the line circuit at back contact 25 so that current cannot flow over the line from battery LB. This marks the end of the conditioning on period and the beginning of the first off period. It will be pointed out at this time that the direct current applied to the line circuit flows through windings and i of relay M, but since these windings are differentially wound the flux produced by the current in winding 3 is neutralized by that produced by the current in winding 4 so that the direct current impulses have no effect upon rotor 6. As will be pointed out in connection with the transmission of indications, the alternating current fiows through winding Ll of relay M and condenser 2C so that the differential effect is not produced by this alternating current flow.

The de-energization of the line circuit at the beginning of the first off period effects the dropping of relays F and FP in sequence and a second stick circuit is closed for relay VP which extends from (-1-), front contact 29 of relay SAP, back contact 39 of relay FP, front contact 49 and winding of relay VP to Relay IV is picked up during the first off period over a 1 circuit extending from (-1-), front contact 42 of relay SAP, back contact 43 of relay FP, front contact 44 of relay VP, back contact 45 of relay 2V and winding of relay IV to Relay IV closes a stick circuit for itself extending from 1 (-1-), front contact 42 of relay SAP, front contact 46 and Winding of relay IV to It will be mentioned at this point that similar stick circuits are closed by the 2V and 3V relays at their front contacts 47 and 48 when they are picked up later in the cycle.

The picking up of relay IV closes a pick-up circuit for relay 2E which extends from (-1-), front contact 50 of relay SA, back contacts 5| and 52 of relays 3V and 2V respectively, front contacts 53 and 54 of relays IV and VP respectively and winding of relay 2E to The picking up of relay 2E opens the energizing circuit of relay IE at back contact 46, which allows this relay to release and again close the energizing circuit for the line at back contact 25, which marks the end of the first off period and the beginning of the first on period.

Relays F and PP are picked up in sequence and relay VP is dropped because its first stick circuit is open at back contact 38 of relay EV and its second stick circuit is open at back contact 39 of relay FP. It will be obvious that relay VPR repeats the operations of relay VP because of front contact 98. The dropping of relay VP 4 opens the circuit of relay 2E at front contact 54 of relay VP, which allows relay 2E to release and close a pick-up circuit for relay IE at back contact M. The picking up of relay IE de-energizes the line circuit at back contact 25 to mark the 4 end of the first on period and the beginning of the second off period,

Relays F and FF are dropped in sequence and relay 2V is picked up over a circuit extending from (-1-), front contact 12 of relay SAP, back contact 43 of relay PP, back contact M of relay VP, back contact 55 of relay 3V, front contact 55 of relay iv and winding of relay 2V to The picking up of relay 2V closes a pick-up circuit for relay extending from (-1-), front contact 50 of relay SA, back contact M of relay 3V, front contact 52 of relay 2V, back contact 54 of relay VP and winding of relay 2E to Relay 2E opens the energizing circuit of relay IE at back contact if allowing this relay to drop and close 6 the energizing circuit for the line at back contact 25 to mark the end of the second off period and the beginning of the second on period.

Relays F and PP are picked up in sequence and relay VP is picked up over a circuit extending from (-1-), front contact 29 of relay SAP, front contact 39 of relay FP, back contact 5'! of relay 3V, front contact 53 of relay 2V and winding of relay VP to Relay VP closes its first stick circuit at front contact 3! and opens the energizing circuit of relay 2E at back contact 5:3, which allows relay 2E to release and close the pick-up circuit for relay IE at back contact The picking up of relay IE de-energizes the line circuit at back contact 25 to mark the end 75 of the second on" period and the beginning of the third off period.

Relays F and FF are dropped in sequence and the second stick circuit for relay VP is completed as previously described. A circuit is now closed for picking up relay 3V which extends from (-1-) front contact 42 of relay SAP, back contact 43 of relay FP, front contact 44 of relay VP, front contact 45 of relay 2V and winding of relay 3V to Relay 2E is picked up over a circuit tending from (-1-) front contact 56 of relay SA, front contacts 5| and 54 of relays 3V and VP respectively and winding of relay 2E to Relay 2E opens the circuit of relay IE at ba .1 contact 40, allowing this relay to release and close the energizing circuit for the line at back contact 25 to mark the end of the third off period and the beginning of the third on period.

Relays F and PP are picked up in sequence and relay VP is dropped because its first stick circuit is open at back contact 5'! of relay 3V and its second stick circuit is open at back contact 39 of relay FP. Relay 2E is dropped because its circuit is open at front contact 54 of relay VP and relay IE is picked up over a circuit including back contact 40 of relay 2E to mark the end of the third on period and the beginning of the clearing out period.

Relays F and PP are dropped in sequence and since there is no other stepping relay to be picked up during this off period, relay lE remains picked up and relay 2E remains down so that the line circuit is held open for a comparatively long interval of time. This allows relays SA and SAP to drop in sequence. The stepping relays are dropped because their stick circuits are opened at front contact 42 of relay SAP and relay IE is dropped because both front contacts 59 and 36 of relays IV and VP respectively are open. The closure of back contact 25 places energy on the line circuit from battery LB so that the next start (oflice or field) can be made at this time.

Relays SR and CD are de-energized during the clearing out period before relay SA is dropped. Relay SR is de-energized by means of a differential circuit closed through its lower winding which extends from (-1-), front contact 60 of relay 3V, back contact 6| of relay VP, back contact 52 of relay FP, front contact 53 of relay CD, front contact 64 and lower winding of relay SR to The oppositely positioned arrows associated with the windings of relay SR indicate that these windings are differentially wound. The dropping of relay SR opens the stick and pickup circuits for relay CD at front contacts I! and !5 respectively.

The SA and SAP relays at the field stations are likewise dropped out during the clearing out period because of the comparatively long deenergization of the line circuit. The particular SO relay which is maintained energized throughout the cycle at the selected station is dropped out during the clearing out period, when the stepping relays are de-energized and front contact I25 of relay 2V is opened. i

Selection of control code.-Jumper I0 (see Fig. 1A), connected as shown, determines that the first impulse applied to the line circuit during the conditioning on period will be (-1-). This is effected by picking up relay PC and dropping relay NC during the preceding initiating period, before the continuity of the line circuit is completed at the end station. The circuit for picking up relay PC extends from (1-), front contact 65 of relay SA, back contacts, and 1380f relays 3V, 2V

and IV respectively, front contact 69 of relay CD, jumper I0 in its full line position and winding of relay PC to The picking up of relay SA and the consequent opening of back contact 65 de-energizes normally energized relay NC.

With relay PC up and relay NC down, the line is energized with a (-1-) impulse over a circuit extending from the (-1-) terminal of battery LB, front contact 30 of relay PC, back contact (H of relay NC, over the previously described line circuit to contact 32 of relay NC, through back contact 32 of relay NC and front contact 33 of relay PC to the terminal of battery LB. In the event that jumper I0 is in its alternate dotted line position, then relay NC will be picked up and relay PC will be dropped and the line will be energize-d with a impulse by way of polechanging contacts 3% to 33 inclusive.

Jumper I I connected as shown determines that the second impulse (first on period) will be because relay NC will be picked up during the first off period over the previously described circuit, which now extends through front contact 68 of relay IV, front contact 70 of relay CD, jumper I I in its full line position and winding of relay NC to In the event that jumper I! is in its alternate dotted line position, then relay PC will be picked up and relay NC will be dropped for making the first on a impulse.

It will thus be seen that the code sending relays are positioned upon the picking up of the stepping relay duringthe off period, while the line circuit is de-energized in readiness for energizing the line with the selected polarity at the beginning of the next on period. Although it is assumed that the station is selected on two steps in the present embodiment, thus requiring code jumpers ID and II, it will be understood that in systems of larger capacity additional code jumpers will be provided and selected on one or more additional steps of the stepping relay bank. The above typical example illustrates how the station selecting code is applied to the line circuit so that any one of two separate code elements are selectively applied for each step of the cycle. These code elements in the present embodiment are (-1-) and The code which is selected during the second off period is determined by the position of lever SML. With this lever in its normal position as illustrated, relay PC is picked up during the second off period, to make the second on impulse (-1-), over the previously described circuit which now extends through front contact 61 of relay 2V, front contact ll of relay CD, lever SML in its right hand normal position and winding of relay PC to In the event that lever SML is in its reverse dotted line position, then relay NC is picked up to make the second on impulse Although the circuit extending through front contact 66 of relay 3V is not shown completed, it will be understood that this circuit may be connected to an additional lever, such as a signal control lever, for determining the polarity of the third impulse. From the above it will be seen that the impulses applied to the line circuit begin with an impulse of alternating current for conditioning purposes, followed by direct current impulses of (-1-) or character dependent upon the code jumper and control lever connections as rendered effective by the particular code determining relay which is picked up for that cycle.

During the clearing-out period at the end of the cycle relay NC is picked up over the previously described normal energizing circuit including back contact 65 of relay SA.

Station. selection for controls-It will be obvious that the impulses are received at all of the field stations, since the field station line relays are all included in the line circuit after the SAP relays pick up to remove the shunt from these line relays at back contacts similar to H3 of Fig. 2. For convenience in describing the operation of station selection, reference will be made to Figs. 2 and 2A which illustrates a typical field station somewhat in detail and which is considered to be the first station of the series and selected by the (-1-) station selecting code applied to the line circuit as previously explained. The field station illustrated in Figs. 2 and 2A is rendered responsive to this particular code because of the connections of jumpers I20 and I2I in their full line positions.

It Was previously explained that relay S0 is picked up during the conditioning 01f period and is stuck up over the previously described circuit including back contact I23 of relay FP At the time that relay FP picks up and opens this back contact, contact I25 of relay F will be in its actuated position, which removes the conductive bridge around back contact I23. Relay S0 is now energized by means of its selective circuit which extends from (CN), front contact IiB of relay 8A front contact I22 of relay S0 conductor 269, back contact I2? of relay 5V jumper 520 in its full line position, -1- bus I253, contact iii; of relay F in its right hand dotted position and lower winding of relay S0 to (13-). By means of this circuit the energization of relay S0 is made dependent upon the polarity of the first (conditioning on) impulse applied to the line circuit, as repeated by relay F actuating polar contact I26 to its right hand dotted position.

In the event that this impulse is then the above described circuit would be incomplete because contact IZfi would not be closed in its right hand dotted position and relay SO would be dropped out. During the first oif period, the dropping of relay F completes the above described stick circuit for relay S0 which may be traced from (CN), front contact H8 of relay SA front contact I22 of relay S0 contact I26 of relay F in its neutral position and lower winding of relay S0 to (B). When relay FP is dropped during the first off period, contact I23 provides a conductive bridge around contact I26, so that this stick circuit is maintained complete until the picking up of relay FP during the next (first) on period.

When relay F1 is picked up during the first on period, relay S0 is maintained energized by means of its selective stick circuit which extends from (CN), front contacts H8 and I22 of relays SA and S0 respectively, conductor 259, front contact I2I of relay IV back contact I28 of relay 2V jumper I2I in its full line position, bus I30, contact I26 of relay F in its left hand dotted position and lower winding of S0 to (B). In the event that the second impulse is (-1-), then contact I26 would be positioned to the right and the second selective circuit for relay S0 would be incomplete, thus dropping out this relay. When relays F and FF are dropped during the second 01f period the above described stick circuit for relay S0 is again completed for maintaining this relay energized until its permanent stick circuit is completed, which is eiiective when relay 2V is picked. up and which extends from (-1-), front contact I25 of relay 2V conductor I68, front contact I3I and upper winding of relay S0 to From the above it will be apparent that code jumpers similar to I20 and I2I of Fig. EA will be provided at other field stations, but connected in different combinations for making these field stations selectively responsive to different codes applied to the line circuit. With the provision of two separate code jumpers in the office and the associated code jumpers at the field stations, four diiferent code combinations are possible in response to the first two impulses applied to the line circuit, three of which may be employed for station selection with the fourth being used for the control phantom code. The system will inherently transmit a series of impulses during the station selecting steps of the cycle if no CD relay in the ofiice is picked up, as a result of the system being initiated from a field station. Tl'ns is because relay STR in the control ofiice is picked up in response to a field start and since no CD relay is picked up, a circuit is completed for maintaining relay NC energized throughout such a cycle, which extends from (-1-) through back contacts of all CD relays, back contact 72 of relay CD of Fig. 1A, front contact I3 of relay STR and winding of relay NC to Transmission of contr0Zs.-It will be recalled that the impulse applied to the line circuit during the second on period was (-1-), as determined by lever SML being in its normal position, this impulse being repeated at the selected field station by relay F positioning its polar contacts to the right. A circuit is cl sed for positioning the polar contacts of relay Ss iR to the right which extends from (13+), contact I32 of relay F in its right hand dotted position, front contact I33 of relay S0 conductor IiS'I, winding of relay SMR back contact Hi l of relay 3V front contacts I28 and I2? of relays 2V and IV respectively, conductor 289, front contact I22 of relay S0 and front contact MS of relay 5A to (CN). Positioning relay S'Mlt to the right closes an obvious circuit at its contact M for energizing switch machine 8M over its normal operating circuit for actuating track switch TS to its normal position.

In the event that lever SML is in its reverse position then the second on impulse is and relay F will be actuated to the left, which Will apply (B) over the above described circuit for positioning polar contact 'M of relay SMR to the left, which will close the r verse energizing circuit for switch machine 8M i'or actuating track switch TS to its reverse position.

In a similar manner additional steps may be used for transmitting additional controls to the selected field station for governing signals by energizing a signal relay, such as relay sG-R with (-1-) or polarities in accordance with the character of the impulses applied to the line circuit as determined by the position of the signal control lever. However, since the above typical examples illustrate the manner of such transmission it is believed unnecessary to point out in detail how the signal control relay or other control relays may be positioned by additional polar impulses.

Following the application of the last impulse, the line circuit is de-energized for a comparatively long interval of time which effects the clearing out of the system in the manner previously described. The stepping relays at the 7 field stations are dropped out in the same manner as explained in connection with those at the control office, since their stick circuits are controlled by the associated SAP relays. It has already been explained how relay S is dropped out during the clearing ou period.

During the operation of a control cycle as above described, no alternating current impulses are superimposed on the line circuit at a field station so that relay M in the control office remains in its neutral illustrated position throughout the cycle. Relay M in its neutral position during the off and on executing periods of the station registration steps of the cycle causes pilot relays IPT and 2PT to be positioned to their neutral positions during such a cycle. Such a code must not register any field station in the office and therefore the contacts of the pilot relays in their neutral positions in combination do not select any station relay. The selection and operation of a station relay for identifying a calling field station in the ofiice will be described in connection with the transmission of indications. In other words, a series of off and on periods of a cycle during which no alternating current is received in the control office at the station selecting steps of this cycle results in an indication phantom code.

Transmission of indica ti0ns.-Although the system is of the duplex type and indications may be transmitted from any station to the control office during the same cycle that controls are transmitted to the same or some other station, it is convenient to first explain the transmission of indications alone on a separate operating cycle, before considering the duplex feature of the systerm.

The manner in which field stations are allowed to transmit only one at a time in a predetermined order will be explained in connection with the look-out feature, this feature being included in the description following the description relating to the transmission of indications from a single field station, assuming that such field station is the only one having new indications to transmit at the beginning of the cycle.

Automatic start-Referring to Fig. 2, a change in the condition of the detector track section or a change in condition of the traffic controlling devices at the station may occur for effecting the initiation of the system for the transmission of indications. Although the detailed circuits are not shown it will be assumed (and readily understood) that any such change may so condition the circuits that relay CH is dropped. The dropping of relay CI-Pimmediately closes a circuit for energizing the line with direct current, which circuit may be traced from the terminal of battery LB in the control office, back contact 30 of relay PC, front contact 32 of relay NC, windings 3 and 4 of relay M, back contact 26 of relay SA, line conductor R, back contact II2 of relay SAP rectifier I00 of unit FWR, upper winding of relay L0 rectifier IUI of unit FWR, back contact I43 of relay CH back contact I44 of relay SA line conductor L, back contact 25 of relay IE, back contact- 24 of relay SA, winding of relay F, front contact 3| of relay NC and back contact 33 of relay PC to the terminal of battery LB.

This direct current energization of the line picks up relay F in the control office and relay L0 at the calling field station. Relay L0 closes a stick circuit for itself which extends from back contacts I35 and I36 .of relays SA and SAP respectively, front contact I31 and lower winding of relay L0 to During the explanation of the look-out feature it will be pointed out how relay L0 is maintained picked up when the above described stick circuit is interrupted at back contact I35 by the picking up of relay SA before relay SAP is picked up to close its front contact I36. For the present however it will be understood that the closure of front contacts I35 and I36 throughout the following cycle maintains the stick circuit of relay LO complete, so that this relay stays up until the clearing out period at the end of the cycle.

Referring to the control office, the picking up of relay F closes a circuit for picking up relay STR which extends from front contact 34 of relay F, back contact 35 of relay SA and lower winding of relay STR to Relay STR closes an obvious stick circuit for itself at its front contact I5.

The picking up of relay STR closes the pick-up circuit for relay SA, which circuit was described in connection with a control cycle but which now extends through front contact I6 of relay STR instead of front contact 20 of relay CD. Relay SAP is picked up over its previously described circuit and during the interval between the picking up of relay SA and the picking up of relay SAP, an impulse of alternating current is applied to the line circuit in the manner previously described. This impulse of alternating current picks up the STR relays at all field stations, after which the SA and SAP relays are picked up. The system now advances through a cycle, during which the line is impulsed and the stepping relay banks are operated as before, with relay NC energized for making the direct current impulses all When the SAP relays at the field stations pick up, the associated STR relays are dropped because their stick circuits are opened at back contacts similar to back contact II4 of relay SAP Although it was not mentioned in connection with a control cycle, it will be understood that the STR relays are similarly dropped out during such a cycle.

Registration of a field station.At the particular station having indications to transmit, lockout relay L0 is up and by means of its front contacts I45 and I46 the indication code transmitting relays IBZ, ZBZ, IFZ and 2FZ are rendered effective. The opening of back contact I63 of relay L0 includes the secondary winding of transformer TF in the line at the transmitting station, so that the combinations of alternating current impulses applied to the primary winding of this transformer by the code transmitting relays will be applied to the line circuit. At all other field stations the lock-out relays will be down and the secondary windings of the associated transformers will be excluded from the line circuit by means of back contacts similar to contact I63.

It will be assumed that the transmitting station illustrated in Fig. 2 identifies itself in the control ofii'ce by a code comprising alternating current of normal phase transmitted during the first off period (following the conditioning on period) and alternating current of reverse phase transmitted during the next (first) on period, as determined by jumpers III) and III in their full line positions. This code combination positions the polar contacts of pilot relays IPT and 2PT to their right and left hand positions respectively for selecting station relay ST, which is the relay for identifying the illustrated station in the control ofiice.

When relay FF is picked up during the conditioning on period the first off indication code is preselected. In the example assumed relay 132 is picked up over a circuit extending from front contact ill of relay FP conductor int, back contacts H8, H9 and Hill of relays cv 2V and 5V respectively, jumper ill] in its full line position, conductor i655, winding of relay i132 and front contact iii? of relay L0 to This indication is transmitted over the line circuit during the first off period when relay FP drops, at which time a stick circuit is completed for relay lBZ extending from (-1-), back contact ill of relay FP front contact l8l and winding of relay IBZ to at front contact Hit of relay L0 Relay lBZ up determines that alternating current of normal phase shall be transmitted over the line circuit. The circuit for transmitting this current impulse may be traced from alernating current supply bus 4, back contact I38 of relay 2132, front contact I39 of relay lBZ, back contact l' l'l of relay F1 primary Winding of transformer TF condenser back contact M8 of relay FF front contact Hi9 of relay IE2 and back contact lat of relay ZBZ to alternating current supply bus 2. The transmission of this alternating current impulse is terminated when relay FP picks up and opens the above described circuit at back contacts Ml and M8. When relay FP picks up to terminate this first alternating current impulse the above described stick circuit for relay M32: is opened at back contact ill and this relay is dropped. In the event that juniper lie is in its center dotted line position, then relay ZBZ would be picked up over the previously described circuit (including jumper H0 in its center position) and relay lBZ would not be picked up, so that pole-changing contacts [38, H39, led and 559 would control the application of alternating current of reverse phase to the line circuit.

The first on indication code is preselected when relay FP is dropped during the first off period. With jumper ill in the position illustrated, relay iFZ is picked up when this selection is made over a circuit extending from back contact ill; of relay FP conductor I64, front contact N5 of relay VP back contact I14 of relay 2V jumper ill in its full-line position, conductor H62, winding of relay ZFZ and front contact i 35 of relay L0 to When relay FP is picked up during the first on period, a stick circuit is closed for relay ZFZ which extends from front contact H6 of relay FP front contact H3 of relay ZFZ, winding of relay 2FZ and front contact Hi5 of relay L0 to This stick circuit is broken and relay ZFZ is dropped during the second of? period, when relay FP drops and opens the above described stick circuit at front contact lit.

An alternating current impulse of reverse phase is transmitted during the first on period (while relay FP is picked up) over a circuit which may be traced from alternating current supply bus i, front contact H2 of relay EFZ, back contact l'lii of relay lFZ, front contact l-lt of relay FP condenser E0 primary winding of transformer TF front contact E il of relay FP back contact ill of relay IFZ and front contact lei of relay QFZ to alternating current supply bus 2. This alternating current impulse is applied to the line circuit by means of transformer TF In the event that jumper ill is in its upper dotted line position, then relay lFZ would be picked up and relay EFZ would be down, so that an alternating current impulse of normal phase Would be transmitted over the line circuit during the first on period. It will be obvious that with jumpers Hi1 and iii in their lower dotted line positions, then neither of the associated relays would be picked up, so that the resulting code would be no alternating current applied to the line circuit.

Referring to the control office, the picking up of relay SAP at the start of the cycle completes an alternating current circuit for winding 5 of relay M at front contact ill. The alternating current impulse of normal phase transmitted over the line circuit during the first cit period, as above described, causes relay M to position its contact to the right. This is because the normal phase alternating current applied to the line circuit extends from line conductor L through condenser ZC, Winding d of relay M and front contacts 2i and of relays SAP and SA respectively to conductor R.

The normal phase alternating current impulse is executed in the control office with relay IV picked up and in the above example results in a circuit being closed from (13+), contact 78 of relay M in its right-hand dotted position, front contacts is and 88 of relays lit and 2E respectively, back contacts 3! and of relays 3V and 2V respectively, front contact of relay EV, upper winding of relay 5?? and back contact 84 of relay lAX to (ON). The polar contacts of relay lPT are positioned to the right and a stick circuit is closed for this relay extending from (B+), contact 85 of relay PT in its right-hand dotted position, lower winding of relay lPT and back contact 84 of relay lAX to (CN). This exeouting circuit is opened when relay lE drops at the end of the first off period, by opening its front contact 79, but relay lPT is maintained in its actuated position by means of the above described stick circuit.

The first on alternating current impulse of reverse phase applied to the line circuit positions relay M to the left and an executing circuit is closed for executing this indication when relay VPR is dropped during the first on period. This executing circuit extends from (B), contact '58 of. relay M in its left-hand dotted position, back contact "i9 of relay lE, back contact 86 of relay VPR, back contacts 87 and 88 of relays 3V and 2V respectively, front contact of relay IV, upper winding of relay 21 T and back contact 93 of relay ZAX to (CN). This results in positioning the polar contacts of relay 2P1 to the left and a stick circuit is closed for maintaining the contacts of this relay in their left hand positions which extends from (18-), contact of relay ZPT in its left-hand dotted position, lower winding of relay ZZPT and back contact 93 of relay ZAX to (CN).

When relay 2V is picked up during the second off period, relay ST is energized over a circuit extending from front contact 95 of relay 2V, polar contact 96 of relay EPT in its right hand dotted position, polar contact 97 of relay ZP'I in its left hand dotted position and winding of relay ST to It will be obvious that other transmitting stations will position these two pilot relays in other combinations of positions for identifying these other stations in a manner which Will be obvious from the above example, considering that a field station may transmit a normal phase, a reverse phase or no alternating current during the first off period for positioning the polar contacts of relay IPT to the right, to the left or to their neutral positions respectively. Similarly a transmitting station may transmit alternating current of normal phase, reverse phase or no alternating current during the first on period for positioning the polar contacts of relay 2PT to the right, to the left or to their neutral positions respectively.

It will be understood that additional steps of the cycle may be allotted for transmitting similar codes in systems of larger size, the number of codes provided being equal to six for one step, thirty-six for two steps, two-hundred and six teen for three steps, etc. It will now be pointed out how the positions of a pilot relay may be changed from its normal to its reverse position or from either its normal or reverse position to its neutral position in response to codes requiring such a change.

The above examples indicated how pilot relays IPT and ZPT were positioned to their right and left hand positions respectively, assuming that their polar contacts were in their neutral positions when the indication codes were received. Assuming that pilot relay IPT has its contacts positioned to their right hand dotted positions, because of a previously established stick circuit including contact 85 in its right hand dotted position, then the reception of an alternating cur rent impulse of reverse phase positions relay M to the left which is effective to de-energize relay IPT by applying (B) to its upper winding over the above described pick-up circuit, for causing current to flow through this upper winding in opposite direction to the current flow through its stick circuit including its lower winding. This differential action de-energizes relay IPT and the instant that contact 85 opens the stick circuit, the executing circuit including the upper winding of the relay is effective to position its contacts to the left.

In the event that relay IPT has its contacts positioned to the left when an alternating current impulse of normal phase is received, then the executing circuit including contact 18 of relay M in its right hand dotted position energizes the upper winding of relay IPT with current of opposite direction to the current flowing through its stick circuit and including its lower winding. This will de-energize relay IPT and when contact 85 opens, the executing circuit is effective to position the contacts of the relay to the right.

In the event that relay IPT is stuck with its polar contacts positioned either to the right or to the left when a code comprising no alternating current is received, then it becomes necessary to restore the contacts to their neutral positions during the executing period. During this executing period (relays IE. and 2E picked up and relay M de-energized), a circuit is closed for picking up relay IAX which extends from (CN), back contact 84 of relay IAX, upper winding of relay IPT, front contact 83 of relay IV, back contacts 82 and 8| of relays 2V and 3V respectively, front contacts 80 and 19 of relays 2E and IE respectively, contact 18 of relay M in its neutral position, front contacts I 09 and I08 of relays IE and 2E respectively, back contacts I01 and I06 of relays 3V and 2V respectively, front contact I of relay IV, winding of relay IAX and contact 85 of relay IPT in either its right or left hand dotted position to (B+) or (B-).

The picking up of relay IAX disconnects ourrent from both windings of relay IPT at back contact 84, which allows relay IPT to restore its contacts to their neutral positions, thus opening the above described circuit including relay IAX so that this relay is de-energized. The above example will indicate how the other biased-toneutral polar pilot relays or indication receiving relays are properly positioned in response to alternating current of normal or reverse phase and in response to no alternating current being received during the executing period. It will be obvious that relays ZAX, 3AX and 4AX are for the purpose of releasing relays 2PT, IIR and HR respectively in the manner described in connection with relay IPT.

Transmission of indications.After thus having registered or identified the transmitting field station in the control office the remaining steps of the cycle are employed for the transmission of indications from the registered station.

With relays M RD and LD in the positions illustrated in Fig. 2A, the second off indication is preselected and relay ZBZ is picked up over a circuit extending from front contact I11 of relay FP conductor I66, back contacts I18 and I19 of relays 3V and 2V respectively, front contact I80 of relay IV back contact I82 of relay M front contact I83 of relay LD conductor IOI, winding of relay ZBZ and front contact I46 of relay L0 to When this selection is made relay IBZ is dropped if up. Relay ZBZ is stuck up when relay FP drops during the second off period, over a circuit extending from back contact I11 of relay FP front contact I84 of relay 2BZ, winding of relay ZBZ and front contact I46 of relay L0 to which stick circuit maintains relay 2BZ picked up throughout the second off period.

An impulse of alternating current of reverse phase is applied to the line circuit during the second off period over a circuit extending from alternating current supply bus I, front contact I38 of relay ZBZ, back contact I49 of relay IBZ, back contact I48 of relay FP condenser IC primary winding of transformer TF (which induces the alternating current into the secondary winding included in the line circuit), back contact I41 of relay FP back contact I39 of relay IBZ and front contact I50 of relay ZBZ to alternating current supply bus 2.

It will be obvious that, in the event that relay RD is picked up and relay ID is down, then the above described circuit would extend through front contact I85 for picking up relay IBZ instead of ZBZ and the above described circuit from the alternating current supply would be reversed at pole-changing contacts I38, I39, I49 and I50 from that previously described.

The second on indication is preselected when relay FF is dropped during the second off period and relay IFZ is picked up over a circuit extending from back contact I16 of relay FP conductor I64, back contact I of relay VP back contact I86 of relay 3V front contact I81 of relay IV front contact I40 of relay WP contact I4I of relay WP in its right hand position, conductor I59, Winding of relay IFZ, and front contact I45 of relay L0 to When this selection is made relay ZFZ is dropped if up. Relay IFZ remains energized throughout the second on period by means of a stick circuit extending from front contact I16 of relay FP front contact I88 of relay IFZ, winding of relay IFZ and front contact I45 of relay L0 to During the following (third) off period this stick circuit is broken by the dropping of relay FP and relay IFZ is de-energized if the next (third) on indication requires its deenergization.

With relay IFZ energized, alternating current of normal phase is applied to the line circuit by means of a circuit extending from alternating current supply bus I, back contact I72 of relay 2FZ, front contact I'll of relay IFZ, front contact M? of relay FP primary winding of transformer TF condenser 50 front contact MB of relay FP front contact llfl of relay IFZ and back contact I69 of relay ZFZ to alternating current supply bus 2. In the event that relay WP has its polar contact Ml positioned to the left, then the above described preselecting circuit would include the Winding of relay EFZ instead of lFZ and by means of the pole-changing contacts of the IFZ and ZFZ relays, alternating current of reverse phase would be applied to the line circuit. In the event that relay WP has its front contact I 40 open, then neither relay IFZ nor 2FZ will be picked up and no alternating current is applied to the line circuit.

It will be obvious from the above examples that a choice of three indications from the transmitting field station is provided to indicate any one of three conditions at each step of the cycle. It will be obvious that, with relay M picked up, the above described preselecting circuits including the windings of relays IE2 and ZBZ cannot be completed because of open back contact I82, thus providing the choice of no alternating current applied to the line circuit during an off period. It will furthermore be obvious that front contacts of stepping relays 2V and 3V may connect to additional preselecting circuits for applying additional indication codes from the trans mitting field station.

To avoid confusion regarding the periods of preselection, transmission and execution of indications, the order of occurrence of these periods will be briefiy pointed out. The first off indication is preselected during the conditioning on period (which follows the initiating period), is transmitted and executed during the first off period. The first on indication is preselected during the first off period, is transmitted and executed during the first on period. The second 01f indication is preselected during the first on period, is transmitted and executed during the second' off period. The second on indication is preselected during the second off period, is transmitted and executed during the second on period. The third off indication is preselected during the second on period, is transmitted and executed during the third off period. The third on indication is preselected during the third off period, is transmitted and executed during the third on period, and so on.

Referring to the control oflice and recalling that relay ST of Fig. 1B is energized in response to the registering of the station in the control office, the reverse phase indication received during the second off period positions relay M to the left in a manner which has already been described. The executing circuit for this indication is completed during the second off period for positioning the polar contacts of relay IIR to the left over a circuit extending from (CN), back contact Hi l of relay 3AX, upper winding of relay IIR, front contact I03 of relay ST, front contact 82 of relay 2V, back contact 8| of relay 3V, front contacts 833 and 19 of relays 2E and IE respectively and contact 78 of relay M in its left hand dotted position to (B). Polar contact Hi2 of relay IIR in its left hand dotted position closes a circuit for lighting lamp LI as an indication that the signal at the field station is cleared for trafilc in a left direction.

It is obvious that an indication code comprising alternating current of normal phase received during the second off period would position the contacts of relay M to the right, which would in turn position the contacts of relay HR to the right for closing the energizing circuit for lamp RI, which would light lamp RI as an indication that signals are cleared for trafiic in a right direction. It is also obvious that the receipt of a code comprising no alternating current during the second off period would position the polar contacts of relay HR to their neutral positions in a manner previously described, which would close an obvious circuit for lighting lamp SI as an indication that the associated signals are at stop.

From the above explanation it is believed obvious how the three on indications transmitted and received during the second on period are effective to position the polar contacts of relay 21R to their right, left or neutral positions for lighting lamps NL, RL or UL as an indication of the condition of the associated track switch.

Loclc-out between field stations.It may happen that changes occur at a plurality of field stations at the same time or in rapid succession so that more than one station will have new indications to transmit at the beginning of a cycle. In order to prevent more than one station actively associating itself with the line circuit during any particular cycle, lock-out means are provided at each station which are effective to select that station nearest the office having new indications to transmit.

It will be assumed that changes occur at sub stantially the same time at the first field station illustrated in Fig. 2 and at the second station from the control office. In this event, relay CH will be dropped and a similar change relay at the second station will be down at the same time. The dropping of relay CH closes the circuit for energizing the line with direct current and picking up lock-out relay L which has already been described. A similar circuit is closed at the second station, including a back contact of the SAP relay similar to contact N2, the associated rectifier unit and the upper winding of the associated lock-out relay, to the line conductor L by way of a back contact of the associated change relay similar to contact i 33. Thus the lock-out relays at both stations will be picked up and stuck up over circuits including back contacts of the SA and SAP relays.

When the SA relay in the control office picks up to apply the impulse of alternating current to the line circuit the SA relays at the stations will pick up, but due to their slow pick-up characteristics the SAP relays will be down for a comparatively long interval of time after their pickup circuits are completed by the picking up of the associated SA relays. During this interval of time alternating current is received at the superior station (illustrated in Pig. 2) and is effective to maintain lock-out relay L0 energized over a circuit extending from line conductor L, front contact 273 of relay L0 back contact 143- of relay CH rectifier unit I55, upper winding of relay LO rectifier unit E52 and back contact l I? of relay SAP to line conductor R.

During this interval (between the picking up of the SA and SAP relays at the field stations) line conductor R extending from the superior station illustrated in Fig. 2 to the second station, is open because of open back contact I53 of relay SA open front contact I54 of relay CH and open front contact II2 of SAP Therefore the lock-out relay at the inferior (second) station receives no current through its upper winding and since the stick circuit including its lower winding is open at a back contact similar to I35 of the associated SA relay, the look-out relay at the inferior station is dropped out. When relay SAP is picked up at the superior station, then the stick circuit for lock-out relay L0 is completed through front contacts I35, I36 and I3! of relays SA SAP and L0 until the end of the cycle.

At the inferior station having indications ready to transmit, the line and line repeating relays will be intermittently energized during the following cycle and the stepping relays will be operated in synchronism with those in the control oflice but the indication conditioning circuits including the relays similar to relays IFZ, ZFZ, IBZ and ZBZ cannot be completed because of open front contacts of the associated lock-out relays similar to contacts I45 and I46.

Although the lock-out feature has been erplained with reference to the station in Fig. 2 having preference over the second station, it will be understood that similar conditions may exist between other preferred and non-preferred stations in the system. It is believed however that the above explanation is sufficient for an understanding of all such combinations, remembering that in each case the station nearest the office which picks up its lock-out relay maintains this relay energized by the alternating current impulse applied to the line from the control office and the other stations beyond the station illustrated in Fig. 2 do not receive this alternating current impulse so that their lock-out relays are dropped out.

The circuit for energizing the upper winding of relay LO was traced through rectifier I SI and I52 and of course referred to the alternating current of one half cycles. For the other half cycles this circuit will be through rectifiers I00 and IIlI so that the upper winding of relay LO always gets current flow in the same direction.

Two-way transmissiO'n.It has been pointed out that control and indication cycles may occur separately or simultaneously. The operations for control and indication cycles alone have been described and it will now be pointed out how the system functions when controls and indications are transmitted during the same cycle. An actuation of the starting button in the ofiice results in the picking up of the associated CD relay. This relay may be picked up at the beginning of a cycle any time up to the end of the period marked off by the picking up of relay SA and the consequent opening of its back contact I4. If a field station has initiated the system, which results in the picking up of line relay F in the control office as previously described, relay STR may be picked up over the previously described circuit any time up to the end of the period marked off by the picking up of relay SA and the consequent opening of its back contact 35.

With relays CD and STR picked up due to ofiice and field starts, the system runs through a cycle of operations as before, but since back contact 12 of relay CD is open and front contacts 69, Ill, II, etc., are closed, the direct current impulses applied to the line circuit are or as determined by the code jumper and lever connections.

The stepping and impulsing operations will be effected as previously described, with the station being selected for controls by the selective energization of the associated SO relay in a manner which has already been explained. Since the look-out relay at the station having indications to transmit is also picked up, the FZ and BZ relays at the associated station will be selectively actuated to apply the indication code, this because of closed front contacts similar to I45 and I46.

The resulting cycle of operations is thus the same, in so far as the transmission of control codes over the line circuit is concerned, as was previously described in connection with a control cycle alone. Similarly the resulting operations during the cycle, in so far as superimposing or not superimposing alternating curent impulses of normal or reverse phases on the line circuit during the off and on periods is concerned, is the same as described for a cycle during which indications alone were transmitted. It is believed that the above brief explanation is sufiicient to indicate that, since the transmission of controls and the transmission of indications are effected by the separate and distinct conditioning of the line circuit, these transmissions may be combined and brought about during a single cycle of operations in the manner previously pointed out.

Having thus described a centralized traffic controlling system, it is desired to be understood that this form of the present invention has been selected to facilitate in the disclosure rather than to limit the number of forms which the invention may assume and it is further to be under stood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice without departing from the spirit of the invention as limited by the appended claims.

What I claim is:

1. In combination with a control office and a plurality of field stations connected by a line circuit, code transmitting apparatus at each of said stations, conditioning means at said office for energizing the line circuit with alternating current, initiating means at each of said stations for causing said conditioning means to initially energize the line circuit with sad alternating current, and lock-out means at each of said stations responsive to the initial energization of the line circuit with said alternating current for rendering the associated code transmitting apparatus effective at only one station at any one time.

2. In combination with a control office and a plurality of field stations connected by a line circuit, code transmitting apparatus at said stations, means at said office for energizing the line circuit with alternating current, means at each of said stations for simultaneously initially energizing the line circuit with direct curent, means responsive to the initial energization of the line circuit with direct current for effectng the en ergization of the line circuit with alternating current, and means responsive to the energization of the line circuit with alternating current for causing the code transmitting apparatus at a preferred one of said stations to operate and for preventing the code transmitting apparatus at the other stations from operating.

3. In combination with a control oilice and a plurality of field stations connected by a line circuit, code transmitting apparatus at said ofiice and at said stations, means at said office for energizing the line circuit with alternating current, means at each of said stations for simultaneously initially energizing the line circuit with direct current, means responsive to the initial energization of the line circuit with direct current for effecting the energization of the line circuit with alternating current, and means responsive to the energization of the line circuit with alternating current for causing the code transmitting apparatus at said ofiice and at a preferred one of said stations to operate and for preventing the code transmitting apparatus at the other stations from operating.

4. In a remote control system; a control office and a field station connected by a line circuit; means in said ofiice for impressing a series of time spaced direct current impulses on said line circuit; a first pair of code transmitting relays at said station; a second pair of code transmitting relays at said station; means controlled by said direct current impulses for successively selecting said first and said second code transmitting relays; automatically controlled means at said station for selectively operating said first and said second code transmitting relays in a plurality of combinations; means controlled by the selective operation of said first pair of code transmitting relays for applying or not applying alternating current of normal or reverse phase to said line circuit during the impression of said direct current impulses thereon, whereby an initial portion of a code is formed; means controlled by the selective operation of said second pair of code transmitting relays for applying or not applying alternating current of normal or reverse phase to said line circuit during the time spaces between said direct current impulses, whereby said code is completed; and a polyphase relay in said line circuit at said oflice responsive to said code for receiving the messages trans-- mitted from said station to said ofiice.

5. In combination with a control oiiice and a plurality of field stations connected by a line circuit; code transmitting apparatus at each station; means controlled by each code transmitting apparatus when rendered operative for trans mitting coded impulses over said line circuit to said office; initiating means at each station for causing an initial impulse of alternating current to be applied to said line circuit; a lockout relay at each station having a line winding connected to said line circuit; means including a one way current device for causing the lockout relay line winding at a particular station to be energized in the same direction by both positive and negative currents from said alternating current impulse, whereby the associated lockout relay is operated; and means controlled by the operation of a lockout relay for rendering the associated code transmitting apparatus operative.

6. In combination with a control office and a plurality of field stations connected by a line circuit; code transmitting apparatus at each station; means controlled by each code transmitting apparatus when rendered operative for transmitting coded impulses over said line circuit to said ofiice; initiating means at each station for causing an initial impulse of alternating current to be applied to said line circuit; a lookout relay at each station having a line winding connected to said line circuit; means including a one way current device for causing the lookout relay line winding at a particular station to be energized in the same direction by both positive and negative currents from said alternating current impulse, whereby the associated lockout relay is operated; a local winding for each lockout relay; means responsive to the operation of a lockout relay for closing and maintaining a stick circuit for the associated lockout relay closed until said coded impulses have been transmitted over said line circuit; and means controlled by the operation of a lockout relay for rendering the associated code transmitting apparatus operative.

'7. In combination with a line circuit energized with either of three different conditions during successive time intervals, a step-by-step means operated one step for each successive time interval, a three-position polar relay for each step, means for energizing each relay with one polarity or the other on its step in accordance with that one of two of the line circuit conditions which is on said line circuit during such step, stick circuit means for each of said polar relays for maintaining it energized with that particular polarity applied during its step until it is energized with the opposite polarity or deenergized, and means for opening said stick circuit means to de-energize each polar relay on its step when the third line circuit condition is on said line circuit during such step.

8. In a remote control system, a communication line circuit connecting a control ofiice and a field station, an alternating current power line connecting said control ofiice and said field station, impulsing means at said control office for impressing a series of time spaced direct current impulses on said communication line circuit, step-by-step means at the control ofiice and at the field station responsive to the direct current impulses on said communication line circuit to operate one step for each impulse during said series to thereby operate through a cycle of operation, an alternating current relay in the control office having a local and a line winding said local winding being directly connected to said alternating current power line and said line winding being connected in series with said communication line circuit, means at said field station for applying alternating current energy from said alternating current power line to said communication line circuit on each step or" said step-bystep means said current having one phase rela tionship or the other with respect to the current in said local winding of said alternating current relay in accordance with whether one indication or another is to be transmitted on that step, a plurality of indication devices at said control ofiice one for each step, and circuit means controlled by said alternating current relay for energizing the indication device for each step in accordance with the relative phase relationship between the currents in the local and line windings of said alternating ctu'rent relay.

WINFRED T'. POWELL. 

